Line of sight (LoS) communication systems are useful for various situations. For example, many cellular telephones communicate via LoS in radio frequency bands. Furthermore, LoS systems may allow for communication to occur after a disaster has struck and other means of communication are unavailable.
Free-space optical (FSO) communications can provide an alternate solution to radio frequency communications for a variety of line-of-sight applications. Due to the continuous desire for increased bandwidth and communication systems, there is interest in utilizing advanced multiplexing techniques to achieve an increase in data capacity in a FSO system. In addition to wavelength division multiplexing and polarization division multiplexing, the use of multiplexing in the spatial domain has attracted a fair amount of attention.
The conventional approach to multiplexing in the spatial domain uses multiple spatially separated transmitter antennas. In such a system, each data-carrying beam is received with multiple spatially separated receivers and the beams are processed to recover the different data streams. This processing may reduce the crosstalk that appears from one beam into the receiver antenna intended for its spatially separated neighboring channel. However, such technology is relatively expensive to implement and the costs increase as the quantity of transmitters and receivers increase.